VerifiableVariable

sample.swift

let userName = VerifiableVariable<String>("") { $0.characters.count > 0 }

userName.isValid
    .bindTo(submitButton.rx.isEnabled)
    .addDisposableTo(disposeBag)

VerifiableVariable.swift

public class VerifiableVariable<Element> {
    public typealias E = Element
    
    private let _subject: BehaviorSubject<Element>
    
    private let _lock = NSRecursiveLock()
    
    private var _value: E

    private let _validation: (Element) -> Bool
    
    public var value: E {
        get {
            _lock.lock(); defer { _lock.unlock() }
            return _value
        }
        set(newValue) {
            _lock.lock()
            _value = newValue
            _lock.unlock()
            
            _subject.on(.next(newValue))
        }
    }

    public var isValid: Observable<Bool> {
        return _subject.asObservable()
            .map { [unowned self] in self._validation($0) }
    }
    
    public init(_ value: Element, validation: @escaping (Element) -> Bool) {
        _value = value
        _subject = BehaviorSubject(value: value)
        _validation = validation
    }
    
    public func asObservable() -> Observable<E> {
        return _subject
    }
    
    deinit {
        _subject.on(.completed)
    }
}